This invention relates to the sensing of oxygen and, more particularly, to a system for measuring the partial pressure of oxygen in a patient's blood.
It has previously been proposed to obtain a transcutaneous measurement of the partial pressure of oxygen in blood by utilizing a so-called Clark type electrode, i.e. an electrode in which a polarographic anode and cathode are immersed in an electrolyte which is interfaced to the environment in which oxygen to be sensed through an oxygen permeable membrane. One such arrangement is disclosed in U.S. Pat. No. 3,795,239 issued to Eberhard et al.
While such prior art units have, to some extent, been successful, the units must be reassembled and allowed to stabilize prior to each use and must likewise be calibrated prior to each use. In addition to this considerable effort which must be gone through each time the apparatus is to be used, the necessary bulk of the electrode system, together with the typical use of a separate heating element, has meant that tight temperature regulation has not been obtainable. Furthermore, the devices have been quite expensive and so bulky and heavy as to interface with their easy application to a patient. Likewise, their cost was such that the medically preferred single use or a throw away type of construction was not feasible.
The oxygen sensor is usually heated by means of a separate heater mounted on the electrode. Often a separate, non-integral temperature sensor is also attached to the electrode. The temperature sensor is used with an external automatic control loop to control the temperature of the sensor very accurately. A high degree of accuracy in temperature regulation is desirable so that the level of oxygen perfusing through the skin is a good indication of arterial blood oxygen partial pressure. In the past, typical oxygen sensing electrodes have been made by machining and molding. Electrodes made in this way have several disadvantages. First, such electrodes are costly in that the manufacture is highly labor intensive; and, second, these electrodes traditionally have poor temperature regulation capability and are bulky and heavy in weight.
Among the several objects of the present invention may be noted a provision of an oxygen measuring system which provides accurate measurement; the provision of such a system which is adapted for oxygen measurement transcutaneously; the provision of such a system providing precise temperature regulation; the provision of such a system in which the sensing elements can be easily applied to a patient; the provision of such a system which can be manufactured relatively inexpensively and in a manner well-suited to high volume production; the provision of such a system in which the electrodes applied to the patient are smaller and lighter in weight than previous electrodes and are inexpensive enough to be disposable. Other objects and features will be in part apparent and, in part, pointed out hereinafter.